Experimental Study on the Damage of Granite by Acoustic Emission after Cyclic Heating and Cooling with Circulating Water

Hot dry rock is developed by injecting cold water into high-temperature rock mass. At the same time, cold water is heated in contact with the rock mass. With the continuous influx of cold water, the surrounding rock will undergo a rapid cooling process, which results in several cycles of heating and cooling. However, there is little research on the influence of cycles of heating and cooling with circulating water on the mechanical properties of rock, which is of great importance to the stability of rock mass engineering in the process of energy development. In this paper, the effects of cyclic heating and cooling with circulating water on the damage of granite are studied using uniaxial compressive, Brazilian and acoustic emission (AE) tests. The results show that heat treatment temperature and number of cycles have important effects on the mechanical properties of granite as follows: (1) at the same treatment temperature, an increase in the number of cycles means that the distribution of physical and mechanical parameters of the granite show an almost exponential downward trend. The uniaxial compression of granite results in its transformation from brittle to plastic, and the failure mode changes from slipping of the shear surface to plastic failure. With increased cycles of heating and cooling with circulating water, the tensile strength of granite also decreases; temperature has an obvious influence on physical and mechanical parameters, cracking of samples, and plays a controlling role in the failure mode of samples. In addition, (2) at the same temperature, the heating and cooling numbers N have a significant influence on the AE distribution characteristics of the sample under uniaxial compression and the number of AE collisions, and the cumulative number of AE decreases with the increase of N. (3) The concepts of mechanical damage and high-temperature and cold-water shock damage during uniaxial compression of samples were proposed based on AE, and the damage equations were established respectively. The curve equations of damage value (D) and cycle numbers N after thermal shock damage of high temperature and cold water were overlaid. The cracking mechanism of high-temperature and cold water impact on granite was analyzed, and the thermal shock stress equation of high temperature and water cooling was established.